Hitherto, an air intake device in which a valve body, bearing members which rotatably support a rotating shaft of the valve body, and air intake ports to which the bearing members are assembled are provided, or the like is known (For example, see Japanese Patent No. 5065211 (Reference 1)).
Reference 1 discloses a bearing device of a butterfly valve (a valve body) which is rotatably incorporated in a valve body (air intake ports) on which an air intake passage portion is formed in a variable air intake device of the engine. In the bearing device described in Reference 1, bearing members which are a separate component are fitted between a rotating shaft of the butterfly valve and a bearing portion (the bearing members) of the valve body side. In other words, the bearing members as a separate component are slidably interposed between the rotating shaft of the butterfly valve and the bearing portion of the valve body side. By applying this bearing structure, each movement (axial shift) of the butterfly valve with respect to the valve body (the bearing portion of the valve body) in a rotating shaft direction and in a radial direction is allowed. By an opening and closing operation of the butterfly valve, an air intake path is switched to a short port and a long port. Accordingly, the engine is closed in the low/mid-rotating region and the air intake path becomes the long port and thus an air intake inertia effect (an air intake pulsation effect) is obtained and an air intake efficiency is kept high.
However, in the bearing device of the air intake device described in Reference 1, since the bearing members as a separate component are interposed between the rotating shaft of the butterfly valve and the bearing portion of the valve body side, many gaps are generated in the bearing structure itself. Therefore, even if the butterfly valve is fully closed, air bypasses gap portions existing within the bearing structure and air is likely to leak from an upstream side to a downstream side of the air intake ports. Thus, since the air intake pulsation (the air intake inertia effect) cannot be efficiently obtained due to sealing properties of the air intake passage portion being lowered, there is a problem that engine performance is lowered.